Amid a truly extraordinary palaver about the identity of the scorer of the all-important goal, one fact remained untroubled by ambiguity.
Never in the history of the Scottish game has a club viewed Hampden as a second home quite like Celtic in three now going on four seasons.
When Neil Lennon takes his side back to Mount Florida on April 11 or 12 to face Aberdeen, it will be the 15th time they have decanted there since 2016. It would be a brave man to wager against a subsequent visit by the time this term is out.
Ryan Christie scored a late goal to send Celtic through to the next round of the Scottish Cup
There was some confusion over the scorer as Christopher Jullien may have got a touch
This slender victory in Perth saw Celtic rack up a 34th successive victory in domestic cups competitions. To suggest they have lately found a way to such affairs is to indulge in stating the blindingly obvious.
Few assignments along the way will have been as arduous as this one. St Johnstone did more than just stay alive until the game ended its closing stages. For long periods, on a truly treacherous surface, they gave as good as they got.
Just nine minutes separated them from the chance to do it all again in Glasgow only for Celtic to continue their happy habit of getting their noses over the line.
Ryan Christie’s free-kick might well have nestled in the rigging in any event. Christopher Jullien took a swipe at it and may even had grazed the ball with his stud.
The confusion and debate over who had the final touch was still raging last night but it will quickly become a mere footnote in this season. Yet again, Celtic prevailed.
The goal came form a free-kick, taken by Christie with Jullien possibly getting a stud on it
Europe may have gone for Lennon’s men for another year but the possibility of a fourth successive Treble is very much alive.
In that regard, you can only admire the huge psychological strength of the champions. The unforeseen home loss to Copenhagen on Thursday was deeply wounding for all concerned but this, the very epitome of a hard-fought win, was just so typical of what the side has produced throughout this extraordinary period of dominance.
Even on a quagmire of a pitch at McDiarmid Park, the energy of the returning Christie still shone through.
Suspended for the European reverse, the midfielder served notice of what was to come by sending an early effort curling just beyond Zander Clark’s far post as Celtic tried to replicate the fast starts of so many of their recent trips to Perth.
Saints had got a deserved point from Rangers seven days previously largely through their manager Tommy Wright pairing Stevie May with Callum Hendry in an orthodox 4-4-2 and that bold approach again asked questions of visitors from Glasgow.
St Johnstone were not without their chances, as Fraser Forster was tested a few times
May’s strong hold-up play allowed his partner to work Fraser Forster with a shot which the keeper only scooped out as far as Matt Butcher. Fortunately for the Celtic keeper, the midfielder’s effort ran harmlessly wide when he ought to have done better.
It was not a day for free-flowing football. With the ball repeatedly sticking in the mud, the completion of four passes was something of an achievement. A crisp exchange between Christie, James Forrest and Leigh Griffiths brought a rare early opening with Scott Tanser standing up strong to bock the latter’s strike.
Odsonne Edouard’s awareness and strength allowed him to find space in behind the home defence with a probing pass. Callum McGregor did well to take the ball in his stride and get his shot away but Zander Clark just about held on.
Saints were not without their moments. Hendry headed a Tanser free-kick just wide of the target before Forster had to backpedal to prevent Drey Wright’s cross dropping in over his head at his far post.
Tensions ran high as both teams battled to try and make it into the next round of the cup
Clear-cut chances remained a rarity. Edouard fired one decent opportunity straight at Clark, the cross having come from Greg Taylor.
A rare Christie error as he tried to drive forward from deep then gifted Wright an unwarranted chance. Forster did well to push the ball away for a corner after the winger had let fly.
Jamie McCart claimed the resultant set-piece from Matt Butcher with a flashing header. Forster took no chances, his extended arm turning the ball over the top.
Bobby Madden refereed the first half with common sense but had no chance to book Butcher and Nir Bitton for fouls on Christie and Hendry, respectively.
Celtic re-emerged for the second period in fresh kits but ruining St Johnstone’s clean sheet was to prove a more difficult task.
Forrest should have at least worked Clark when smartly played in by Christie but he dragged his effort inches beyond the far post.
Neil Lennon will be hoping for a more convincing performance in the semi-finals
When Jason Kerr let a long punt run through his legs, he could only look on in horror as Edouard dribbled his way to goal. Just when it seemed Clark’s net would finally bulge, the Frenchman slipped, sending his shot off target.
Wright always looked St Johnstone’s most likely source. Having led Taylor a merry dance down the right, his centre looked destined to present May with a tap-in until Jullien’s sliding intervention.
An error always looked like the most likely means of this tie being settled at the first time of asking. Having spilled Forrest’s effort, Clark must have feared he’d provided one only the ball to roll just beyond Griffiths.
Griffiths’ last action before making way for Tom Rogic was to find the stand with his normally trusty left foot, the spadework coming from Kristoffer Ajer’s surge up the middle.
The Australian’s introduction preceded Celtic’s first concerted spell of pressure. McGregor’s mazy run through the centre ended with Christie firing a loose ball just wide.
Christie then drew an excellent stop from the Saints keeper, the opening fashioned by a succession of one-twos between Rogic and Edouard.
An extraordinary sequence saw Clark beat away Edouard’s shot before Jullien’s attempt at converting the rebound was somehow deflected wide of the post.
St Johnstone performed well but Celtic have a habit of winning important matches
Ajer’s needless foul on May presented Saints with a gilt-edged chance to edge in front. Tanser, unforgivably, smashed the free kick straight into the wall. The Norwegian defender did soon redeem himself, though, with an excellent block to deny May converting from 12 yards.
McGregor’s involvement appeared to be in jeopardy when Nir Bitton inadvertently hammered the ball at his arm but he soldiered on.
Just as Saints were beginning to think this was their day, disaster struck. McCart’s cynical foul on Forrest broke up a promising counter-attack but didn’t banish the danger completely.
Christie’s in-swinging free-kick was textbook. Jullien might just have got a feather of a touch to guide the ball away from Clark but so much of the credit went to the midfielder for a sumptuous delivery that might well have gone in in any event.
Liam Gordon became the last man to have his name taken by Madden for a high challenge on Jullien that on another day might well have merited a red.
Saints gave it everything. But as many as a side has discovered over the past four years, where Celtic are concerned, even that is not enough.